The present invention relates in general to sewing machines and in particular to a new and useful apparatus for monitoring the supply of thread in a rotary hook or shuttle by utilizing a photodetector which also serves as a pulse generator which is used in conjunction with counting means.
A household sewing machine according to U.S. Pat. No. 4,432,297, has means for turning on an indicating device as soon as the thread reserve on the bobbin has fallen below a certain amount. With the indication of a predetermined remainder of thread, the operator will be able, with certainty, to complete a started job before the shuttle thread is used up. But such a measure has the disadvantage that usually a considerable remainder of thread is left on the bobbin to be changed, which must be removed before a new bobbin is filled. In addition, the shuttle thread capacity is not sufficiently utilized. To use such an arrangement in commercial sewing it is desirable, therefore, to use up the remaining shuttle thread as much as possible.